Why it matters

Historically, JQuery was important during the browser wars because browser vendors implemented the DOMAPI standard inconsistently, and JQuery was the best way to ensure consistent behavior across them. That is less relevant nowadays as browsers gradually converge.

Today, It is arguable whether you should be using JQuery in your projects. On one hand, it makes development easier, but it also requires downloading a large javascript library on your site which can slow down page load times. It is good to know JQuery because you are bound to run into it, but my personal opinion is that if you should avoid it when you don’t absolutely need it.